1. Field of the Invention
This invention relates to the art of producing hydrocarbons from a subterranean formation and more particularly, to a process for fracturing a high permeability subterranean formation and controlling fluid-loss which results in higher regained formation permeability upon completion of the process.
2. Brief Description of the Prior Art
In the fracturing of subterranean formations for the production of hydrocarbons, it is common to produce fractures in the formation by pumping a fluid at a relatively high pressure into the formation through a wellbore whereby the formation fracturing pressure gradient is exceeded and fractures propagate from the wellbore into the formation. Nearly any fluid given enough volume and pressure can be used to fracture a subterranean formation. However, fracturing fluids, generally include a viscosifying or gelling agent such as a polysaccharide material, such as for example, a natural or synthetic gum such as guar or hydroxypropyl guar or a derivatized cellulose such as hydroxyethylcellulose to affect the rheology and increase the proppant carrying capability of the fluid. These fluids are often referred to as "linear gels." Additionally, the fluid-loss control and proppant transport capability can be effected by the use of crosslinking additives incorporated into the fracturing fluid. Some well known crosslinking agents include borates, titanates, zirconates, antimony and other organometallic compounds such as described in U.S. Pat. Nos. 3,888,312, 4,021,355, 4,502,967, 5,165,479, 5,271,466 and 5,304,620.
Each of the crosslinked fracturing fluids has its own particular advantages. Borate crosslinked systems generally are considered to be less damaging to fracture conductivity because the gels generally can be broken more efficiently and removed from the formation. Borate fluids, however, generally are usable only at lower temperatures (below about 300.degree. F.) because of thermal breakdown during use. Titanium and zirconium crosslinked fluids generally exhibit better temperature stability, but generally are believed to be more damaging to the formation if incomplete breaking of the gel occurs.
Stimulation in high-permeability formations, that is formations having a permeability greater than 10 millidarcy (&gt;10 md), has generated considerable interest in recent years. Attempts have been made to utilize hydroxyethylcellulose (HEC) as a viscosifier in the fracturing fluids. Unfortunately, HEC and most other linear gels exhibit high rates of leak off to the formation because they may not build up a satisfactory filter cake with acceptable volumes of lost fluid at permeabilities &gt;10 md. This results in large volumes of fluid being required for each formation treatment. The high fluid-loss also makes it very difficult to create a fracture having the desired geometry to maximize hydrocarbon production.
Because of their ability to build filter cakes, even in high permeability formations, crosslinked fracturing fluids demonstrate better fluid-loss control. However, these filter cakes can be more damaging to the formation production capability than linear gels through damage to the proppant bed permeability and by invasion into the formation.
It would be desirable to provide a method by which a high permeability formation could be successfully stimulated while minimizing the potential for formation and proppant bed damage.